Same problem here on a TS253-Pro.But since this problem only arises when shutting down the server (also automatic shutdown at a specific time) I doubt there will be something found in the dvblink log-files.There's a .force_kill_in_shutdown.log on qnap system and this shows:

So there's a dvblink process that has to be force killed as it doesn't shut down as requested when the NAS is shutting down.The dvblink log files set to info don't show anything at the same time point.

I have the same problem, I have to upgrade the "Volume" to a "thick Multiple Volume" instead of a "Static Single Volume" and I got in trouble. I also have a problem with two tuners, it can only find one. Both seem to work, but not simultaneously. It feels like 4.2 is not so stable for DVBlink.Qnap TS-451 firmware 4.2.0 01/01/2016 DVBlink 5.5.0 with two tuners TV-Butler